Measurement System for Evaluating Dielectric Permittivity of Granular Materials in the 1.7–2.6-GHz Band

The design and the experimental characterization of a waveguide system for complex permittivity measurements on both solid and granular materials are presented. The proposed system is intended for the dielectric characterization of asphalt concrete and of its components at frequencies around 2.45 GHz. Therefore, the system provides measurements on granular materials, such as mineral aggregates found in the asphalt concrete. A series of experimental tests on reference materials shows, via comparison with a standard measurement system, errors within 1%. A theoretical analysis of uncertainty contributions confirms a predicted expanded uncertainty lower than 2%. Furthermore, to test the proposed system for dielectric spectroscopy on materials typical of the asphalt industry, measurements were also performed on calcareous and basaltic materials, which are typically used for the production of asphalt. Finally, three different dielectric models (namely, α model, Ansoult's model, and Topp's equation) were comparatively assessed to identify the most suitable ones in describing the water content and dielectric permittivity relationship for the considered materials.